The present invention relates to a color ink for thermal ink-jet printing, and, more specifically, to a color ink comprising an improved decap agent that improves the decap time of the ink without affecting the color-to-black bleed control.
Ink-jet printers are commonly used in offices and homes because of their low cost and high print quality. Recently, ink-jet printers capable of printing images in both black and color have been developed. To print color images, the printers use a combination of cyan, magenta, and yellow inks to produce the colors of the color spectrum. Color ink-jet inks are typically aqueous based and are formulated by dissolving a colorant, such as a dye or pigment, in an ink vehicle. For example, a yellow ink would comprise a yellow dye or pigment dissolved or dispersed in an ink vehicle. Color dyes and pigments are known in the art. The dyes used in color inks are typically present in salt form and are designed to form solids in a substrate, such as a paper substrate, by crystallizing the dye on the substrate. The ink vehicle may also contain numerous other components, as discussed herein, depending on the application and desired properties of the color ink-jet ink.
Typical commercial ink-jet printers contain at least 4 inks, one being black and the other three being, cyan, magenta and yellow. When color and black ink areas are printed adjacent to each other, for example, on graphical diagrams, it is important to keep a good edge definition, or bleed, between the colors and the black.
Regardless of the application, a color ink-jet ink should have good print qualities. An optimal color ink would have a long decap time, low color-to-black bleed, low color-to-color bleed, a fast drying time, high resistance to light fade, and a long shelf-life. However, there is usually a tradeoff between achieving these properties because improving one property results in the deterioration of another property. In particular, there is usually a tradeoff between optimizing decap and bleed control in color inks.
The term xe2x80x9cdecapxe2x80x9d refers to the ability of the ink-jet ink to remain fluid upon exposure to air. The decap time of the ink is measured as the amount of time that an ink printhead can be left uncapped before the printer nozzles will clog or plug. The nozzles can become plugged by a viscous plug forming in one or more of the nozzles, by crusting of the ink, or by crystallization of the dye in or around any of the nozzles. If a nozzle has plugged, ink droplets ejected through the nozzle""s orifice may be misdirected, which may adversely affect print quality.
If the orifice is completely blocked, ink droplets may not pass at all through the affected nozzle. Decap times of ink-jet inks are typically measured over short and long periods of time. The short time decap is an important factor that determines how long the printhead can print without xe2x80x9cspittingxe2x80x9d. Because not all the nozzles of the printhead print all the time, the printer service routine requires the idle nozzles to spit on a regular basis into the waste container (spittoon) to avoid printing defects. It is desirable, therefore, to keep the short-time decap as long as possible because it improves throughput and saves inks. On the other hand, long-time decap determines how long a printhead can be stored in an uncapped state. In particular, it determines such attributes of the printhead as the storage stability. A preferred color ink would be able to be left uncapped and unused for extended periods of time without plugging.
A preferred ink would also have low color-to-black bleed properties. Bleed is the dye diffusion that takes place when one ink dot is printed next to another. When multiple colors are printed on the paper, the colors may bleed into one another as the colors mix on the surface of the paper or within the paper. To have optimal print quality, it is preferable that the colors do not mix with each other or with black ink. In addition, it is preferable that there is a clean border between colors and between colors and black ink.
Various solutions have been disclosed to improve the color-to-black bleed of color inks, including adding heat sources to the printers, developing special papers, and increasing the penetration rate of the color ink into the paper.
While various solutions have been proposed that improve decap or color-to-black bleed control of color inks, the prior art is silent about improving one of these properties without affecting the other property. Since these two properties are usually inversely related, it would be advantageous to develop a color ink-jet ink that has improved decap but does not affect color-to-black bleed control.
In accordance with the invention, a color ink-jet ink is provided in which decap is improved without affecting the color-to-black bleed control of the ink. This is accomplished by adding an improved decap agent to the color ink-jet ink. The improved decap agent comprises a multivalent salt of a perchlorate anion, where the cations of the perchlorate anion include calcium, manganese, magnesium, zinc, aluminum, and iron. The specific color ink-jet ink formulated in accordance with the invention displays improved or unchanged decap without affecting the color-to-black bleed control of the ink.
A method of using the color ink-jet ink is also provided. The method comprises formulating the color ink-jet ink comprising about 0.1 to 10 wt % of an improved decap agent comprising a multivalent salt of a perchlorate anion. The color ink-jet ink is applied on paper, adjacent to black ink-jet ink. The color ink-jet ink achieves improved decap of the color ink-jet ink without affecting color-to-black bleed control.
In addition, a method of improving decap without affecting color-to-black bleed control of a color ink-jet ink is provided. The method comprises formulating a color ink-jet ink comprising about 0.1 to 10 wt % of an improved decap agent comprising a multivalent salt of a perchlorate anion.